Radio crystal detector



April 30, 1929. MCMURTRY 1,711,174

RADIO CRYSTAL DETECTOR Filed March 22, 1925 Patented Apr. 30, 1929.

NETED STATES PATENT- OFFICE.

EDWARD ALEXANDER MCMURTRY, OF CHICAGO, ILLINOIS.

RADIO CRYSTAL DETECTOR.

Applieationfiled March 22, 1923. Serial No. 626,815..

My invention relates to crystal detectors for use in radio receiving sets and the obects of my invention are first, to provide new and improved constructions for said detectors whereby a crystal detector may be mounted on the back of the panel of a radio set and adjusted for sensitivity by the simple rotation of a knob and dial or other manually operated means on the front or control side of the panel; and second, to provide improved contact members for said detectors, which do not require visual adjustments or direct manual application, or poking around, upon the crystal surface; and which cannot become disengaged from or thrown out of contact with the crystal, or caught in the irregularities of the crystal or mounting there of, or otherwise cease to function properly as the detector is adjusted by the turning of the knob and dial on the front of the panel.

I attain these objects bythe mechanism illustrated in the accompanying drawing in which Figure 1 is a side view of my invention, Figure 2 is a perspective view of the same from the back of the panel, Figure 3 is a detailed representation of improved contact members, Figure 4 shows a rotating 0011- tact construction.

Similar numerals refer to similar parts throughout the several views. '1

' Panel 19 represents a part of the panel of a radio set and is generally of hard rubber or other insulating material. Cup 5 with set screw 6 is used as a retainer for the crystal 7 which ma be of silicon alena or an other substance known and used at presentin crystal detectors, for its rectifying properties. Attached to cup 5is shaft 2 which extends through a hole in panel 19 as shown, and a knob and dial 1 is secured to shaft 2 by means of set, screw 3. The

knob and dial is on the control or front side of the ancl. Washer 4t acts as a saacer t 77 CC 77 between dial 1- and panel 19 Metalstrip 8 of li 'ht SJ11110 brass orcoa 301 has two l holes drilled therein, one to pass shaft and the other to pass screw 9. Screw 9 and nut 10 tightened down upon terminal con nector 11 form one terminal of-the detector.

Spring contact member 12 shown 111 detail in Figure 3 a is made of llght flexlble spring copper ribbon about three thou sandths of an inch in thickness and about inch wide. Ribbon of brass or hard aluminum or similar metal will serve equally well. It is punched asshown, hole 21 and eyelet 20being-of such size that screw will'pass through them freely. Eyelet permits the smooth operation of spring 12 up and down screw 15 as thumb nut 18 is turned. A plurality of contact projections are embossed in the free end of spring 12,

as shown at 13, and these contacts serve to engage the surface, of the crystal 7. Terminal connector 14 is securely bolted to the. back of panel 19 by nut 16 on screw 15. Screws 9 and 15 have their heads countersunk below the front surface of panel 19and are obscured from view by the dial 1. Spring contact 1.2 is securely held between nuts 16 and 17 through hole 21. Eyelet 20is slipped over the top of screw 15 and thumb nut 18 is screwed down until some of the contact projections 13 engagethe crystal, and then about one half turn more is given the thumb nut 18 to obtain the correct contact pressure on the crystal. i

The contact member may be adjusted or moved laterally, and set to any desired position, over the crystal, or to one side thereof to permit removal of the crystal from its cup, by first looseningthe nut 17 to permit the desired adjustment and then again tightening it to hold the contact member in the position to which it has been set. If desired and then the spring member 12 carrying the contact is carefully bent so that the contact point or points are a short distance, sayabout a sixteenth of an inch, below the level of the crystal surface. Then upon adjust ing the contact member over the crystal and securing it by-the clamping nut 17 the contact point will be found to bear upon the crystal surface with the desired light pressure. I This is an extremely accurate as well as simple method of regulating the pressure of the contact point 13. f r The crystal is mounted'so as to projec slightly above the rim of the cup 5. I If the crystal is mounted in soft metal it mustproj ect somewhat above the surface of the metal so that contacts 13 do not touch any metal and thereby short circuit thedevice renderin it temporarily inoperative. The contact shown in Figure 3 c is serviceable, having a pad of metal woo-l or finely matted conducting material soldered or Otherwise secured to the spring 12 in place of the contacts 18, to engage the crystal surface. In Fig ure 3 d is shown a crystal retaining cup soldered to the back of the spring strip 12 and a hole through the said strip corresponding with the hole in the cup permits the crystal to be mounted in the cup Ell and secured by the set screw 26. \Vith a cup so attached, the spring strip "'12 is of somewhat heavier material than for the other kinds of contacts because of the weight of the cup'and crystal. which must be supported. In Figure 3 L is shown a single point contact embossed in the form of a llattened cone or pyramid which may be used with a crystal mounted even with or beiow the sin-face of the metal mounting and, like all of the con. tact forms described above, will operate sn'iooth'ly and without mechanical or electrica fault with the smoothest or most irregular ofcrystals or mountings and is a notable advance in contact construction for crystal detectors.

hen a crystal of bornite is mounted in cup 24; and used in coniunction with a crystal of copper pvrites mounted in cup 5, the combination is what is universally known as a perikon detector.

Figure 4: shows a contact member made of metal ribbon 12 the same as for the contacts shown in Figure a, 7) and c. It is ient as shown and secured to a shaft '2 by means of nuts 28 and 29 and takes the place of the cup 5 of: Figure 1. This may be used in conjunction with contact member cl Figure 3. The plurality of contact points 13 are shown, but this may be like 5 or c Figure 3 for the contact surface. 'lhis an arrangement involving a rotary or moving: contact with a stationary crystal mounting. It is obvious that the panel 15) indicated in the accompanying drawings, may be either the panel of the radio set proper, or a small individual panel forming part of the detector element of the radio In the latter event the knob and dial 1 would be adj usted outward upon tl c shaft 2 sulliciei ...y far to permit the usual panel to lie between the dial and the anel 19, and suitable means, such as the bolts 9 and 15, would be employed to unite the two panels.

The detector is adjusted for sensitivity by slowly rotating, the knob and dial 1 on the front or control side of the panel. "lefer ring to Figure 1, this causes cup 5 and crystal 7 to rotate and contact points 13 explore the surface of the crystal as it moves under them.

Any crystal detector circuitmay be em ployed and in this respect it is no differentfrom any crystal detector now in use. It may be used wherever crystal detectors find a use, in conjunction with. audion sets, in wave-meters, ct cetera.

The universal practice up to the present time of mounting a crystal detector on the front of the panel has barred it as a part of any line audion set, and made it none the less desirable on a crystal set, for its mechanism has been not only crude and unsightly, but for its adjustment it required a tedious poking; around directly on the crystal surface with various kinds of coil sirings or catwhislter wires that have kept the crystal detector in the class of unreliable toys.

In the particular embodiment of my invention illustrated in the drawings the [latspring 12 serves a means for limiting the lateral movements of the contact point or points asthe crystal is being moved or rotated beneath such contact or contacts. But other suitable means may be employed. for limiting the lateral movements of the contact point and still come within the scope of my invention, and possess some of the advantages thereof. My invention overcomes all of these defects, and with its ease of adjustment, and simple knob and dial control, and back panel mounting it is worthy of a place on the finest set.

I claim broadly the following constructions and combinations,

1. In combination with a panel, of a crystal detector compri a crystal, a mounting therefor, an electi c terminal connected with the crystal, a resilient spring; carrying a contact adapted to engage with the surface of the crystal, means for adjusting the spring to regmlate the pressure between the contact and the crystal, means tor restricting the lateral movements of the contact upon the crystal, the parts of the detector enumerated being located atthe back of the panel, a l-znob located at the front of the panel for adjusting the relative osition of engagement of the contact with the crystal, and means for establishing electrical connection with the said contactspring.

2. In combination with a panel, of a crystal detector comprising: a crystal, a mounting; therefor. an electric terminal connected with the mounting, a resilient spring carrying a ated being located at the bacir ot the panel,

a knob located'at the front of the panel for rotatingsaid crystal mounting, and means for establishing,- electrical connection with said resilient spring.

EDWARD ALEXANDER McMURTRY. 

